1. Field
The present specification generally relates to petroleum processing and, more specifically, to methods for demulsifying an emulsified petroleum source using carbon dioxide without precipitation of petroleum components such as asphaltenes during the demulsification.
2. Technical Background
Oil in water (o/w) and water in oil (w/o) emulsions cause many problems in the petroleum industry and require attention from the oil producers during the recovery, treatment, and transportation of crude oils. Emulsion breaking is always a challenge for the oil producer and the refiners. Currently, crude oil is the most important hydrocarbon resource in the world, and heavy crudes account for a large fraction of the world's potentially recoverable oil reserves. Heavy crude oils presently account for only a small portion of the world's oil production because of their high viscosities that cause problems during transportation. Nevertheless, increasing needs for addressing the concerns related to heavy crude oils cannot be avoided, because the supply of light crude is dwindling all across the globe.
Usually, crude oil is considered to be a colloidal dispersion of asphaltene and resins, which constitute the discrete and polar components, dispersed in a continuous phase made of non-polar compounds. Crude oil may also be described as a heterogeneous, complex organic mixture predominantly composed of saturated and aromatic hydrocarbons. It also contains heteronuclear compounds, emulsified water, and other inorganics. The hydrocarbon portion contains normal alkanes, isoalkanes, cycloalkanes, and aromatics (mono-, di-, and polynuclear aromatic hydrocarbons (PAHs) with alkyl side chains); resins (aggregates with a multitude of building blocks such as sulfoxides, amides, thiophenes, pyridines, quinolines and carbazoles); and asphaltenes (aggregates of extended polyaromatics, naphthenic acids, sulfides, polyhydric phenols and fatty acids) with thousands of assorted derivatives. The asphaltenes are colloidal in nature and the atomic H/C ratios ranges between 1.0 and 1.2 and N, S, and O content of a few weight percent implying that a large segment of the asphaltene backbone is constituted of fused aromatic carbons interspersed with polar functional groups containing five to seven heteroatoms per macromolecule. Asphaltenes do not have a specific chemical formula. Individual asphaltene molecules can vary in the number of atoms contained in the structure, and the average chemical formula can depend on the source.
Asphaltenes are typically present in micelles within crude oil. When crude oil is recovered as an emulsion such as an o/w emulsion or a w/o emulsion, for example, the protective shell of the micelles may be broken down, causing the asphaltenes to agglomerate or precipitate. Agglomerated or precipitated asphaltenes are notorious for fouling or clogging production equipment in the petroleum industry. Accordingly, ongoing needs exist for methods to demulsify petroleum sources such as crude oil, particularly asphaltene-rich heavy crude oil, without agglomeration or precipitation of asphaltenes.